Comparative Study of Expression of Smad3 in Oral Lichen Planus and Normal Oral Mucosa

Oral lichen planus (OLP) is a chronic inflammatory disease of the oral mucosa which is considered by the World Health Organization (WHO) as a premalignant condition. One step in malignant development is so called epithelial mesenchymal transition (EMT), a process whereby epithelial cells acquire mesenchymal characteristics. A factor known to induce EMT is the transforming growth factor-β (TGF-β), which uses the Smad proteins as mediators for its signaling. The aim of this study was to compare the expression of Smad 3 in Oral Lichen Planus and normal oral mucosa. This descriptive analytic study was performed on 30 patients with OLP (21 women and 9 men with mean age of 45.23± 2.44 years) and 20 normal oral mucosa (14 women and 6 men with mean age of 46.95± 2.21 years). The samples were studied by immunohistochemical staining. Data were analyzed with paired T-test and Wilcoxon test by SPSS software. Expression of Smad3 in OLP samples and normal oral mucosa was different. This difference was statistically significant (P<0.001). The apparently higher expression of Smad 3 in oral lichen planus compared to normal oral mucosa might help to discuss its higher potential for malignant transition.

ichen planus (LP) is a relatively common chronic dermatologic disease that often affects the oral mucosa with a prevalence ranging from 0.2 to 4% (1)(2). Indeed Oral lichen planus (OLP) is considered as a chronic disease with dynamic evolution (2) for which several panels of diagnostic criteria, such as the modified WHO one, have been diagnosis (3). The cause of LP is unknown; it is generally considered to be an immunologically mediated process (4). Hence, there is a questionable theory about the potential of OLP for malignant transformation into oral squamous cell carcinoma (OSCC) (5). Although Gonzalez-Moles et al. (6) have reported the frequency of 0 to 12.5% for this kind of transformation, in a recent study, Shen et al. (7) demonstrated that the incidence of OSCC developing in lesions previously diagnosed as OLP, is less than 1% and they didn't entirely rule out these cases as de novo OSCCs.
Transforming growth factor β (TGFβ) regulates several cellular processes including proliferation, differentiation, migration and death (8) (11). Therefore, in this study we investigated the immunohistochemical (IHC) expression of Smad3 in tissues with OLP and adjacent normal tissues to determine the relative role of this protein in evolution of OLP and evaluate the prognostic value of this marker when the progression to malignancy is suspected.

Tissue specimens and clinical data
Our study consisted of 30 biopsy specimens taken from patients with OLP (24 reticular and 6 erosive), as defined by modified WHO criteria (3) and 20 samples of non-inflammatory, nonprecancerous adjacent normal oral epithelium as  Table 2).

Discussion
We designed the present study in order to evaluate Epithelial-Mesenchymal Transition (EMT) changes in oral lichen planus because of malignant behavior of this disease and its tendency to change to head and neck squamous cell carcinoma (HNSCC) which was found in previous studies.
Among the proteins which have role in EMT, we chose Smad3 because it is involved in TGF-β pathway and is highly expressed in several cancers (12). The SMAD genes encode components of the TGF-β signaling normally inhibits the cell cycle; the loss of these genes may allow unrestrained cell growth (4). Smad3 together with co-factor SNAIL also acts in repression of E-cadherin and Occludin which help tumoral progression (13). Smad3 may have a role in apoptosis and also in inflammation, but the results are contradictory (14)(15).  In this study, we found a higher expression rate in OLP compared to normal oral mucosa which was statistically significant (P<0.001). Different In the present study, expression was seen in the nucleus of epithelial cells which is explained by Smad3 active status due to phosphorylation.
Considering normal oral mucosa, we found few cells with Smad 3 expression which is in accordance with Danielson et al.'s study results (11), but is in contrast to the study of Karatsaidis who found a strong expression of Smad 3 in normal oral mucosa (10).
As a whole, our findings showed an increased expression of Smad 3 in OLP compared to normal oral mucosa which might be due to its probable role in apoptosis, inflammation and EMT and may indicate its higher potential for malignant transition.